Crayon Physics is one of the most wonderful things I have seen lately. It lets you actually BE Harold from Harold and the Purple Crayon (but you have MANY crayon colors to choose from!).
Is it a good game? I dunno...it's really easy to just sort of brute force your way through most levels, but even then it's completely charming. You owe it to yourself to at least grab the demo and play it through. If it makes you want to get a tablet computer with a digitizer though, don't blame me.